The overall goal of this research project is to better understand the relation between physiological measures of temporal and spatial interaction in cochlear implants (CIs) and performance on psychophysical and speech-perception tasks. Speech-processor program parameters such as stimulation rate, number of electrodes, or stimulus timing (i.e., simultaneous or sequential stimulation) can be manipulated to some extent to reduce interaction in either the temporal or spatial domain. However, it is not clear what the relative contributions of temporal and spatial interaction are to speech-perception ability and how these effects vary across individual CI users. It is possible that interaction affects CI recipients in different ways based on differences in peripheral physiology. Further, differences in peripheral physiology may account for differences in performance as a function of programming choices across individual CI recipients. It is anticipated that research findings from this project may translate into objective methods that can be used to choose specific CI speech-processor programming parameters to maximize performance on an individual basis. This research project consists of three specific aims. The first aim is to evaluate the extent to which physiological measures of auditory-nerve temporal response properties relate to psychophysical measures of temporal integration and performance with different rates of stimulation. These studies will evaluate temporal response properties of the auditory nerve, temporal integration ability, and speech-perception performance with different rates of stimulation. We hypothesize that neural measures such as refractory-recovery and stochastic independence will aid in predicting an optimal stimulation rate for individual CI users. The second aim is to examine the extent to which physiological measures of spatial selectivity are related to pitch ranking and electrode discrimination for intermediate (or virtual) channels. These studies will evaluate the relation between physiological measures of spatial selectivity using actual and virtual channels versus pitch ranking and electrode discrimination tasks. We hypothesize that measures of auditory-nerve spatial selectivity will aid in predicting whether intermediate pitches can be perceived for individual CI users. These measures may lead to objective ways to determine whether an individual subject may benefit from a strategy that employs expanded spectral representation through intermediate or virtual channels. The third aim is to examine the relative effects of physiological and psychophysical channel interaction for simultaneous and sequential stimulation. These studies will evaluate the relative contribution of each type of interaction to determine whether the potential benefits of increased stimulation rate outweigh potential disadvantages of electrical field interaction with simultaneous stimulation. We hypothesize that physiological measures may aid in predicting whether better performance is achieved with a fully sequential strategy versus a partially simultaneous strategy. The goal of this research is to find objective ways to choose speech-processor programming parameters for cochlear implant recipients. The benefits are that recipients would be fit with an optimal program from the beginning of implant use. This is especially important for very young congenitally deafened children who cannot actively participate in formal speech-perception testing or sound-quality judgments, which are traditionally used to determine the best program for an individual.